Neutrinos: nimble subatomic superparticles

As a member of that select group known as ''elementary particles,'' neutrinos are considered to be among the most fundamental constituents of matter. As an atom disintegrates, it gives off energy. Scientists were puzzled when they found that atoms, when they decayed in a certain way, seemed to radiate less energy than they should. This couldn't, they reasoned, for it violated law of physics: the conservation of energy.

Then they found the particle that balanced the equation: the neutrino. In beta-decay, these minuscule bits of pure energy are shot off at the speed of light.

At the frantic pace of light speed, neutrinos have no mass, as Albert Einstein's famous equation, E EQUALS mc2, predicted. Another quality of these subatomic particles is their ability to penetrate other matter. They can zip through the equivalent of 3,500 light-years' worth of lead without hitting anything. Atoms are huge, clumsy things next to the nimble neutrinos.

Physicist Wolfgang Pauli first introduced the idea of this particle in 193l. Physicist Enrico Fermi dubbed them neutrinos in 1934.